Heat exchangers may be employed in conjunction with gas turbine engines. For example, a first fluid at a higher temperature may be passed through a first passageway, while a second fluid at a lower temperature may be passed through a second passageway. The first and second passageways may be in contact or close proximity, allowing heat from the first fluid to be passed to the second fluid. Thus, the temperature of the first fluid may be decreased and the temperature of the second fluid may be increased.
Counter-flow heat exchangers provide a higher efficiency than cross-flow type heat exchangers, and are particularly useful when the temperature differences between the heat exchange media are relatively small. Conventional heat exchangers with a plurality of tubes have drawbacks with regard to the connection and formation of numerous inaccessible tubes with small spacing.
The helical tubes must be arrayed without interruption in order to form a closed helical flow channel and to thereby ensure operation in true countercurrent flow with high efficiency. However, the assembly of tube bundles with contiguous helical tubes and their connection become particularly problematic as the number of tubes increases and were hitherto at best possible with a very small number of helical tubes.
As already mentioned, the manufacture of tube bundles of this type becomes particularly problematic when the number of tubes is increased inasmuch as the connection of the contiguous tubes becomes particularly difficult due to the inaccessibility of the tube ends and therefore is not possible with conventional connecting means. It is further particularly difficult to bend rigid tubes into exactly contiguous coils and to connect them by conventional connecting means.